Furnace wall structure



Feb. 26, 1935. F TONE I I 1,992,5zw

FURNACE WALL STRUCTURE Filed July 8, 1951 rill/1111111111111.

INVENTOR I FRANK I TONE ATTORNEY Patented Feb. 26, 1935 UNITED STATES PATENT OFFICE FURNACE WALL STRUCTURE Application July 8, 1931, Serial No. 549,415

8 Claims. (01. 1226) This invention relates to furnace wall structures such as are used in boiler furnaces (and the like) of the type in which the side walls are subjected to severe temperature conditions. The

invention relates particularly to a composite type of wall consisting of refractory material in which are installed fluid-containing tubes to absorb a portion of the heat and prolong the life of the structure.

The present invention relates more particularly to methods of furnace wall construction in which the refractory blocks are urged toward and againstthe fluid tubes and means for holding them in this intimate contact. This application is filed to cover subject matter divisible from my previous Patent No. 1,775,414. v

Various means may be employed in urging the refractory blocks into intimate contact withthe furnace wall tubes. I do not limit myself to any one method as I have found that the desired results may be obtained by employing mechanical, gravity, or thermalexpansion means of obtaining a desired thermal contact.

The invention may be readily understood by reference to the accompanying drawing, which illustrates preferred embodiments of my invention;

but to the details of construction of which my invention is not limited.

In the drawing:

a furnace wall embodying my invention;

. Figure 2 is a view similar to Figure 1 showing a slightly modified construction of refractory block;

35 Figure 3 is a section taken along the line III-III of Figure 1, showing portions of the inner and outer walls of the furnace;

Figure 4 is a view similar to Figure 2, showing a modification of the metal strap shown in Figure 2;

Figure 5 is a view similar to Figure 1 showing a modification in which the strap consists of a bimetal material;

Figure 6 is a horizontal section of a portion of a furnace wall, showing a modification of my invention; and

Figure 7 is a section taken along the line VII-VII of Figure 6. r

In the construction shown in Figure l, the refractory block is made with a lug which may be inserted into the wall structure in a direction normal to the face of the wall. In this construction, 10 represents the body of the block and 11 is 9. lug provided thereon which is sufficiently wide to flll the space between the two par- Figure 1 is a horizontal section of a portion of allel fluid tubes 3. The lug extends rearwardly as far as the inside edge of the tube and is provided in one face with a groove 11a into which a metal strap 12, preferably of resilient metal, may be set. This strap 12 engages the two parallel 5 tubes to urge the blocks into intimate contact with said tubes and consequently improve the heat transmission as well as the mechanical stability. By making the straps 12 of sufiicient widths, it is possible to have a single strap hold 10 two adjacent blocks in place. This can be done by forming the groove 11a in one of the blocks on the top face of the block and having the groove correspondingly located in the bottom of the block which would be superimposed thereon. The 15 two grooves would then be opposite each other and would be aligned so that the single strap 12 could serve to hold two blocks in place, as shown in Figure 3.

The construction shown in Figure 2 is gener- 20 ally similar to that described in connection with Figure 1, but in this particular form of block the body 13 of each block has two legs or lugs 14 which are spaced apart a distance suflicient to enable the block to straddle the tube or pipe 3. The width of the lugs or legs 141s equal to substantially half of the distance between the adjacent tubes, so that the lugs of two adjacent blocks will serve to fill the gap between two adjacent tubes. The lugs 14 are provided with grooves 15 arranged in the same manner as the grooves 11a described in connection with Figure 1. A strap 16, preferably of resilient metal, may be inserted in the grooves 15 of the legs of the adjacent blocks, to urge the blocks into. intimate contact with the furnace wall tubes and improve the heat transmission and mechanical stability.

In the modification shown in Figure 4 the con-' struction of the refractory article may be identical with that described in connection with Figure 40 2. In this modification an adjusting means is provided to vary the tension of the spring strap 21 and the resulting contact pressure between the curved face of the refractory block 13' and the fluid tubes 3. The adjusting bolt 22 is threaded through the strap 21 and engages the rear wall of the tube 3 thus urging the refractory back against said tube and maintaining a good thermal contact. A lock'nut 23 may be used to lock the adjusting bolt 22 in the adjusted position. Slot 15' corresponds toslot 15 of Figure 2.

The construction shown in Figure 5 provides a thermal expansion means of maintaining an intimate contact between the refractory block 10' and the fluid tube 3'. The construction is my similar to that shown in Figure 1, with the exception that the strap 31 is composed of a bi-" metal material. This bimetal strap is of the well known variety in which two dissimilar metals, having different coeflticients of expansion,

are integrally joined. A change in temperature causes unequal expansion of the two metals and results in a deflection or bending of the bimetal strap. In the form shown in Figure 5, any deflection due to an increase in temperature causes the curved-bimetal strap to tend to straighten thus exerting a pull on the refractory block and urging it into more intimate contact with the fluid tube. It is understood that the less expansible component of the bimetal strip lies adjacent the fluid tubes in the construction shown.

Another method of utilizing thermal expansion means to decrease the contact resistance to heat flow between the refractory blocks and the fluid tubes, is shown in Figures 6 and 7. In this form of structure the tubes 3' are enclosed by a pluralityof refractory blocks 44 and 45 of right and left hand construction as shown. A wedge shaped block 41 engages the recessed inclined surfaces 42 and 43 of the refractory blocks 44 and 45 respectively. This wedge 41 is composed of a material having a greater coefficient of expansion than the refractory blocks. Thus any increase in temperature of the wall as a whole causes the wedge 41 to expand more rapidly than the refractory blocks 44 and 45. Such expansion produces horizontal movement of said blocks, thereby forcing thecurved surfaces of the semicircular recesses 46 and 47 into more intimate contact withthe fluid tubes.

In the operation of boiler furnaces it is desirable to keep the temperature of the refractory furnace'lining below the temperature at which it would react with the molten coal ash or slag, and in fact form a layer of congealed slag next to the refractory. Where high furnace temperatures are encountered such as that usually found in oil or pulverized fuel installations, the furnace walls are generally cooled by a fluid medium which passes through tubes or ducts located in the refractory lining. In such installations the furnace lining serves as a protective covering for the furnace wall tubes and also as a heat conductor to transmit part of the heat to the fluid tubes,

'where it is absorbedin a useful manner. In such installations the rate of heat transfer should be such that asuflicient amount of heat will be withdrawn from the exposed portion of the refractory block to keep it below the temperature at which it would react with the products of combustion.

By increasing the intimacy of contact between the refractory blocks and the fluid tubes I have been able to obtain a considerable increase in heat transfer and a desired temperature gradient through the refractory lining. Experimentally, I have found that the thermal conductivity and resulting flow of heat through a silicon carbide furnace lining to a fluid container can be increased more than 30% by increasing the contact presstn'e from one to eleven pounds per square inch. Further increase inpressure beyond that value causes a much slower increase in heat flow per pound increase in pressure.

While the refractory blocks used in connection with my invention may be of any suitable refractory material, I prefer to use a material having an especially'high degree of refractoriness and a high coeihcient of thermal conductivity or heat permeability as compared with fire-clay. This is due to the fact that I have found these properties enable a suflicient amount of heat to be withdrawn from the exposed face and to produce a desired temperature gradient through the refractory lining which causes the molten slag to congeal and form in a thin layer over the entire face of the refractory. This layer of slag acts as a protective coating and prevents further reaction of the refractory with the products of combustion. When the heat, which is conducted away from the exposed portion of the refractory blocks. reaches the back of said blocks it is absorbed by the fluid passing through the furnace wall tubes and utilized in a useful manner. There is, therefore, a very definite advantage obtained by the use of refractory blocks of high heat permeability in combination with cooling tubes and in intimate thermal contact with said tubes, whereby a more highly refractory furnace is secured and a more effective cooling of the lining obtained.

As a specific example, silicon carbide has been found to be from around six to nine times more thermally conductive than fire-clay. The ther- 'mal conductivity as compared with fire-clay varies according to the density of the refractory blocks, the manner in which they are formed,

and the percentage of bonding material and filler relative to the amount of silicon carbide contained in the blocks. Silicon carbide is also very much stronger at the high operating temperatures of a boiler than fire-clay. The thermal conductivity of silicon carbide .is well above .006 cal/cm /C./sec. whereas fire-clay has a thermal conductivity well below this;

I claim:

1. In a fluid-cooled furnace wall, the combination of fluid-circulating conduits, a protective coating of refractory blocks therefor, and resilient metal straps partially embedded in said blocks and contacting said conduits constantly urging said refractory blocks into intimate contact with said fluid conduits.

2. In a fluid-cooled furnace wall, the combination of fluid-circulating conduits, a protective coating of refractory blocks thereover, and members so arranged that their thermal expansion urges said refractory blocks into intimate contact with said fluid-containing conduits as the temperature of said wall increases.

3. In a-' furnace wall structure. refractory blocks consisting mainly of silicon carbide in superincumbent relationship, cooling conduits adjacent said blocks, and means automatically tending to urge said blocks and conduits into continually closer juxtaposition whereby the heat transmission between said blocks and conduits is permanently improved and whereby said urging tendency is not substantially diminished by thermal expansion of the members comprising the wall as the furnace is heated.

. 4. A furnace wall comprising highly conducting refractory blocks shaped to contact with water pipes, said blocks having curved slots therein, and resilient bimetal strips whose intermediate portions are received in said slots and whose outer ends contact with said water pipes, the constituents of the bimetal being so chosen that increase of temperature tends to move the blocks and pipes into relatively closer contact.

5. In a furnace wall, fluid-containing tubes for cooling the wall, highly conducting refractory blocks in contact with adjacent surfaces of a pair of tubes, and a thermally expansible member which is arranged to cause said blocks to exert a pressure against said tubes and increase pressure as the wall is heated.

6. A furnace wall structure, comprising a fluidcirculating conduit, a protective refractory coating thereover, and means constantly forcing said coating and said conduit into intimate contact with one another, wherein the said forcing is not substantially diminished by thermal expansion of the members comprising the wall, as the wall is heated.

7. In the operation of furnaces having fluid cooled walls composed of fluid circulating conduits and refractory blocks thereover, the methsaid 0d of increasing the mechanical stability of said wall and improving the transmission of heat to said conduits which comprises continuously urg- 3 ing said blocks and conduits sition and maintaining the pressure of blocks against. conduits substantially undiminished as the wall is heated.

8. In the operation of furnaces-having fluid cooled walls composed of fluid circulating conduits and refractory blocks thereover, the meth- 0d of increasing the mechanical stability of said wall and improving the transmission of heat to said conduits, which comprises urging said bloclm against said conduits by means of members the thermal expansion of which prevents substantial diminution of the pressure of the blocks against the conduits as the wall is heated.

FRANK JEROME TONE.

into closer juxtapo- 

